1. Field of the Invention
The present invention generally relates to an optical information recording medium and a recording strategy generation method therefor, and especially relates to a phase-changing type optical information recording medium such as CD-RW, DVD-RAM, DVD-RW, and DVD+RW, and a recording strategy generation method therefor.
2. Description of the Related Art
In recent years and continuing, demands for high-speed recording using an optical information recording medium are increasing. Especially, since an optical disk-like recording medium is capable of raising recording and reproduction speeds by making rotational speed high, improvements in the speed are progressing. Since recording on the optical recording-medium is carried out by optical beam intensity modulation, a simple recording mechanism realizes optical recording, hence the medium and the mechanism can be provided economically. Further, since the intensity modulated optical beam is used in reproducing, high compatibility with a reproduction apparatus is secured. For this reason, the optical recording has been widely used, and the demands for even higher speeds and higher density are appearing along with demands for large capacity storage of electronic data.
Among such optical disks, disks that employ a phase-changing material are widely used, because they can be rewritten a large number of times. In the case of the optical disk that uses a phase-changing material, recording is carried out by applying an optical beam that is intensity modulated to a layer material. The layer is suddenly cooled such that it assumes an amorphous state, and the layer is gradually cooled such that it assumes a crystalline state. Since optical physical properties of the amorphous state differ from those of the crystalline state, optical information is recorded.
Since sudden cooling and gradual cooling are used, recording at a high speed is carried out by irradiating a recording optical beam that is three-value intensity modulated as disclosed by Japanese Provisional Publication No. H9-219021. As an actual recording method, a method disclosed by Japanese Provisional Publication No. H9-138947, Japanese Provisional Publication No. H9-219021, Recordable Compact Disk Systems Part III (commonly known as Orange Book Part III) version 2.0, ditto volume 2 version 1.1, and DVD+RW Basic Format Specifications version 1.1 will be herein below illustrated.
By the recording method disclosed by the above-mentioned documents, a mark as shown by (a) in FIG. 24 is recorded as follows. Where the mark is present, it is represented by a High signal, and where there are no marks (i.e., where there is a space), it is represented by a Low signal as shown by (b) of FIG. 24. The time length of the mark and the space is defined as n times a basic clock period T. In other words, the time length of the mark is expressed by nT. The range of n, a natural number, depends on modulating methods. Specifically, in the case of CD systems, n is between 3 and 11; and in the case of DVD systems, n is between 3 and 11, and 14. FIG. 24 shows the case of n=6.
According to the conventional technology as described above, in order to form the mark of the time length nT, a multi-pulse containing m pulses is irradiated as shown in (c) of FIG. 24. The number m is dependent on n, and is defined as m=n−1 or m=n−2. The definition is derived from the minimum value of n being 3 in the cases of CD and DVD. Further, an irradiation cycle of the pulse is set at 1T as shown in (c) of FIG. 24, which is the case of m=n−1. The same is said of the case of m=n−2, i.e., irradiation cycle of the pulse is set to 1T as shown in (d) of FIG. 24. In either of these cases, however, the cycle and the width of the first cycle are uniquely set up (different from the other pulses).
This recording method is considered to be suitable for the mark length recording method, since only an addition of a pulse is necessary for a mark that is longer by 1T.
However, when a faster recording speed is required, the basic clock frequency has to become high, for example, about 104 MHz for a 24×CD-RW, and about 131 MHz for a DVD-RW and DVD+RW, which are equivalent to 5×. With such a high clock frequency, considerable portions of the irradiation period are consumed by rising and falling of an irradiation pulse, lowering effective irradiation energy, i.e., an integrated value of the irradiation by the conventional recording method (recording strategy) as shown by FIG. 25.
In FIG. 25, dotted lines indicate ideal irradiation waveforms, and solid lines indicate simulated actual waveforms. Time period consumed by rising and falling of the pulse is shown in (a) of FIG. 25. As the basic clock frequency is raised as shown in (b) of FIG. 25, a ratio of the rising time and a ratio of the falling time to the whole period become higher, and for this reason, a peak power Pw becomes not high enough, and a bottom power Pb becomes not low enough. That is, the peak power Pw is lowered by ΔPw, and the bottom power Pb is raised by ΔPb. The lower peak power Pw can raise temperature of only a small volume of the layer material, therefore, only a small volume of an amorphous domain can be formed. The higher bottom power Pb suppresses sudden cooling, therefore, re-crystallization will be promoted, and the volume of the amorphous domain will be decreased as a result. Therefore, the small volume of the amorphous domain causes a fall of reproduction signal amplitude, and reproduction reliability is remarkably degraded.
In order to solve the above-mentioned problem, a optical beam source (a laser diode and its drive) that is capable of providing a beam with short rising time and falling time is required. For a clock frequency exceeding 100 MHz, the rising time and the falling time have to be 1 ns or less, which is difficult to obtain.
Then, technology (later technology) that carries out high-speed recording with the present luminescence optical beam source is proposed by Japanese Provisional Publication No. H9-134525 and U.S. Pat. No. 5,732,062 specification, wherein the number of recording pulses is reduced. According to the later technology, in order to form a mark having time length nT, m pulses are used, where m fulfills n=2m if n is an even number, and n=2m+1 if n is an odd number, comparing with the previous technology that uses (n−1) pulses when making the nT long mark. More specifically, in the EFM (eight-to-fourteen modulation) method adopted by CD-RW, according to the previous technology, since n is a natural number selected from 3, and 4, 5, 6, 7, 8, 9, 10 and 11, the number of irradiation pulses is 2, 3, 4, 5, 6, 7, 8, 9, and 10, respectively. In contrast, in the later technology, to n=3, 4, 5, 6, 7, 8, 9, 10 and 11, the number of irradiation pulses is set to 1, 2, 2, 3, 3, 4, 4, 5, and 5, respectively, that is, the number of the irradiation pulses becomes about one half of the previous technology. As shown in (c) of FIG. 25, the irradiation period of one pulse is expanded from about 0.5T (in the case of the previous technology) to about 1T in the later technology, alleviating adverse influence of the rising time and the falling time.
Since a 2mT long mark and a (2m+1)T long mark are recorded by the same number of pulses, the irradiation period cannot be a constant. In order to differentiate the two marks, the irradiation period (period of P=Pw) and the cooling period (period of P=Pb) of a pulse of the 2mT long mark are shortened.
Japanese Provisional Publication 2001-331936 discloses a recording method using m multi-pulses in order to form an nT long recording mark, wherein a ratio n/m is set as being equal to or greater than 1.25, and describes in detail the technology for recording a 2mT long mark and a (2m+1)T long mark by the same number of pulses m, like the case of the Provisional Publication No. H9-134525. As for the method for differentiating length of marks formed by irradiating the same number of pulses of this technology, the irradiation period and the cooling period of the first pulse, and the irradiation period and the cooling period of the last pulse are adjusted.
The method of differentiating length of marks formed by irradiating the same number of pulses basically requires that the irradiation period and the cooling period of all the pulses be defined to each mark length. EFM (eight to fourteen modulation) used by the compact disk requires 69 parameters to be defined; and EFM+ (a kind of 8–16 modulation) used by DVD requires 77 parameters to be defined. Techniques are proposed in order to reduce the number of parameters to be defined, namely, a technique of unifying the irradiation period of the first pulse regardless of n where m>=3, a technique of unifying the irradiation period and the cooling period of a middle pulse (i.e., a pulse except the first pulse and the last pulse) where m>=3, etc. However, in the cases that m=1 and m=2 (i.e., n<=5), it is considered necessary to set up parameters uniquely for each of the cases. Therefore, in order to define a recording luminescence waveform (recording strategy), a large number of parameters are needed. Furthermore, when recording speed (scanning speed) differs, a different pattern for every recording speed is needed, which is considered solvable by defining a unified constant absolute irradiation period where P=Pw, which is not depending on recording speed (not a value relative to the clock cycle that changes with recording speed but an actual period of pulse width).
Further, in the case of the write-once type and re-writable optical disk, typically, CD-R/RW and DVD+RW/R, it is common to pre-format the parameters concerning disk recording conditions on the disk itself. Examples of pre-formatting the disk recording conditions are information recorded in ATIP (Absolute Time in Pregroove) Extra Information of CD-R/RW, and Physical Information recorded in ADIP (Address in Pre-groove) of DVD+RW/R. The information contains scanning speed, optimum recording power, parameters required in order to compute the optimum recording power from a test recording, parameters for specifying optimum recording strategy, and the like, in addition to basic parameters such as the kind of disk and the version of the base standard. As for the parameters for specifying the optimum recording strategy, the standards document of CD-RW sets forth ε(=Pe/Pw) and Strategy Optimization (dTtop, dTera); and the standards document of DVD+RW sets forth Ttop, dTtop, Tmp, dTera, ε1 and ε2.
An information recording apparatus reads the information, when recording on the disk, and determines the recording strategy. Therefore, while it is desirable that the parameters are prepared in detail in order for the information recording apparatus to set up an exact recording strategy, the amount of the information should not be extremely large. Especially, in the case of a CD-R/RW system, the amount of information (capacity) that can be pre-formatted is limited to 21 bits×6=126 bits. When additional information should be provided, it is necessary to record the additional information using a pre-pit, using a domain newly defined in the innermost part or the outermost part of the disk, for example, XAA (Extra Additional Information Area) adopted by CD-R Multi-speed, etc.
The information recording apparatus reads the pre-formatted information prior to starting the recording operation as mentioned above, and optimum recording strategy is set up. Therefore, if a large number of parameters are set up for every disk, process becomes complicated, and a strategy generating circuit becomes complicated.
Accordingly, it is desired that an exact strategy be generated with a least number of parameters.